Carbon nanotubes (CNTs) have significant attention due to their mechanical, thermal, and electrical properties. Recently there have been significant research activities regarding development of CNT/polymer nanocomposite materials. CNT/polymer nanocomposites have shown promise in applications such as electromagnetic interference (EMI) shielding, photovoltaic devices, and gas sensors.
For example, CNT/polymer nanocomposites are highly sought-after candidates to replace traditional metal and metal alloys for aircraft manufacturing. However, significant limitations still exist which prevent the potential of these nanocomposites from being fully exploited. In the fabrication of nanocomposite materials, a good dispersion and adhesion of nanofillers with polymer matrices generally play an important role towards obtaining nanocomposite materials with expectant and reproducible properties and performances. However, the as-produced CNTs are held together in bundles by strong van der Waals interactions. The bundling interferes with CNT dispersability and results in diminished electrical and mechanical properties of the nanocomposite as compared to theoretical predictions. Also, the commercially available samples generally contain a significant concentration of impurities, such as amorphous carbon and catalytic metal particles used for conventional nanotube synthesis.
Most nanotube purification methods involve nitric acid treatment. This treatment leads to oxidation of the CNT outer walls, causing disruption of the conjugated electronic structure and sometimes shortening of the CNTs. As a result, the electrical conductivity and the aspect ratios of CNTs purified by nitric acid tend to decrease.
Other than strong acid treatment, a wide range of non-destructive chemical modification methods have also been reported to obtain increased dispersion of CNTs in solution. However most of these methods involve the use of surfactants or other chemicals to assist in the dispersion process. After the nanocomposite materials are processed and dried, the surfactants and chemicals generally remain in the final composite material as additives, which can significantly adversely affect the resulting properties of the composite material.